Ouedraogo Mamadi^1,, Dao Amidou¹, Diallo Seydou¹, Kamagate Bamory¹, Noufe D. Djibril¹

The Aghien Lagoon watershed belongs to the hydrographic system supplying drinking water to the Abidjan metropolitan area in southern Côte d'Ivoire. This study aims to quantify and map the dynamics of soil water erosion in this watershed over the period 1987-2023, using remote sensing and geographic information systems. The Revised Universal Soil Loss Equation (RUSLE) was applied, combining five factors: rainfall erosivity (R), soil erodibility (K), slope length and steepness (LS), vegetation cover (C) and support practices (P). The R factor was estimated from CHIRPS data for four dates (1987, 2003, 2015 and 2023), and the C factor from the corresponding land-use maps. The results show a continuous worsening of erosion: the mean soil loss rises from 22.8 to 59.8 t ha⁻¹ yr⁻¹, while the area subject to extreme erosion expands from 1.2% to 13.7% of the watershed. This dynamic coincides with the retreat of dense forest from 32.4% to 9.0% of the watershed, the fourfold increase of bare soils from 6.6% to 26.8%, and the rise of the mean C factor of emerged land (from 0.26 to 0.44), combined with record rainfall erosivity in 2023 (R = 368.17 against about 228 over 1987-2015): vegetation cover degradation appears as the main driver of erosion, amplified by recent rainfall forcing. These results help identify priority areas for erosion control, within a perspective of sustainable management of a strategic peri-urban watershed.

Erosion, Remote sensing, GIS, RUSLE, Aghien Lagoon, Côte d'Ivoire